Add environments reading (#13701)

### What problem does this PR solve?

environment variable > config file

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

internal/admin/handler.go

@@ -473,7 +473,14 @@ func (h *Handler) ListRoles(c *gin.Context) {
 		return
 	}
 
-	success(c, roles, "")
+	if roles == nil {
+		roles = []map[string]interface{}{}
+	}
+
+	success(c, gin.H{
+		"roles": roles,
+		"total": len(roles),
+	}, "")
 }
 
 // CreateRoleHTTPRequest create role request